The present invention provides a crystalline 2-hydroxynaphthalene-3-carboxylic acid having significantly suppressed dusting tendency, and a process for preparing the same.
2-hydroxynaphthalene-3-carboxylic acid is important as an intermediate for pigments or dyes. Generally, it is prepared by reacting xcex2-naphthol with sodium hydride to give sodium xcex2-naphtholate, reacting the resulting compound with carbon dioxide under pressure to give sodium 2-hydroxynaphthalene-3-carboxylate and then, isolating the desired compound by means of acid precipitation i.e. by adding a mineral acid to the salt.
For a long time, the Kolbe-Schmitt reaction, a solid-gas phase reaction, had been employed for the reaction between sodium xcex2-naphtholate and carbon dioxide. Said reaction, however, had some problems, such as more than 50 hours of long reaction time was required, high amount of xcex2-naphthol was wasted because of thermal heterogeneity at the high reaction temperature, controlling the reaction was difficult due to the phase conversion and a stable yield was hardly obtained. In order to solve those problems, a number of methods including a method using reaction media had been proposed.
One of the present inventors had invented a process comprising the step of reacting a liquid mixture consisting of light oil or kerosene, sodium xcex2-naphtholate and xcex2-naphthol, with carbon dioxide (Japanese Patent Publication (KOKOKU) No. 53296/1981) and said process has been industrially used at present. This process can be carried out successively and can provide 2-hydroxynaphthalene-3-carboxylic acid with very low amount of impurities and with highly stable quality. According to said method, 2-hydroxynaphthalene-3-carboxylic acid with high quality, such as those having 220-221xc2x0 C. of melting point and 99.5% of purity and containing only 0.03% of sodium xcex2-naphtholate, can be obtained. In the process, 2-hydroxynaphthol-3-carboxylic acid is isolated from the mother liquid by means of acid precipitation, filtration, centrifugation and the like, washed with water, dried and then, is used as an intermediate for pigments or dyes.
Crystalline composition of 2-hydroxynaphthalene-3-carboxylic acid usually comprises very fine particles and, therefore, is highly dusty. In addition to the dusting tendency, due to the severe mucosal irritativeness of 2-hydroxynaphthalene-3-carboxylic acid, handling of the compound is highly obstructed. For example, when 2-hydroxynaphthalene-3-carboxylic acid is added into a reaction tank as an intermediate for a pigment or dye, fine particles of 2-hydroxynaphthalene-3-carboxylic acid fly in the air as powdery dust. The fine particles of 2-hydroxynaphthalene-3-carboxylic acid flown in the air are hardly precipitated, disperse widely, pollute the environment, and stimulate the skin and mucosa of the operators to make them uncomfortable. In order to diminish the problems concerning workability and safety in the feeding step, operators wear dust-proof glasses and masks and the reactor is mounted a vacuum at a position other than the supply port to deaerate the fine particles and a filter to trap the same. However, they are not enough.
The reason why 2-hydroxynaphthalene-3-carboxylic acid dusts significantly is believed that said compound consists of very fine crystalline particles, and that said compound is hardly dissolved in water and, therefore, hardly uptakes moisture; and therefore, each crystalline particles do not agglomerate or bind together through the free water. As a consequence, the fine crystalline particles move individually upon an external impact. In order to suppress the dusting tendency of the material having the above-described characteristics, Japanese patent Application Laid Open No. 196841/1983 discloses a method for granulating 2-hydroxynaphthalene-3-carboxylic acid particles. Although thus obtained granulated 2-hydroxynaphthalene-3-carboxylic acid particles exhibited suppressed dusting tendency, said process is highly complicated, that is, comprises the steps of adding a determined amount of water to 2-hydroxynaphthalene-3-carboxylic acid and controlling the water content of acid precipitated 2-hydroxynaphthalene-3-carboxylic acid by centrifugation and therefore was not suitable for mass production.
Further, Japanese Patent Application Laid Open NO. 212533/1986 discloses a process for preparing granule comprising the step of granulating 2-hydroxynaphthalene-3-carboxylic acid together with an aqueous mixture containing a hydrophilic organic solvent having lower boiling point such as a lower alcohol. In this process, the step to add the organic solvent is required and therefore, the whole process becomes longer.
Accordingly, the object of the present invention is to solve the above-mentioned problems and to provide crystalline 2-hydroxynaphthalene-3-carboxylic acid with well-suppressed dusting tendency.
The present invention provides a crystalline composition of 2-hydroxynaphthalene-3-carboxylic acid with a extremely suppressed dusting tendency, having an average particle size of equal to or more than 175 xcexcm and the proportion of the particles of which particle size are equal to or less than 74 xcexcm is equal to or less than 14%.
In the present specification and claims, each xe2x80x9c%xe2x80x9d represents weight % except for indicated particularly.
In the present specification and claims, the average particle size means the value determined as below:
The sample material is weighted and then is sequentially screened with sieves having aperture of 710 xcexcm, 297 xcexcm, 170 xcexcm, 106 xcexcm, 74 xcexcm and 45 xcexcm in this order. The residue on the respective sieves and the amount of passed the 45 xcexcm sieve were weighed. The average particle size is calculated as follows:
average particle size (xcexcm)=(710xc3x97residue on the 710 xcexcm sieve (wt %)/100)+(297xc3x97residue on the 297 xcexcm sieve
(wt %)/100)+(170xc3x97residue on the 170 xcexcm sieve (wt %)/100)+(106xc3x97residue on the 106 xcexcm sieve (wt %)/100)+
(74xc3x97residue on the 74 xcexcm sieve (wt %)/100)+(45xc3x97residue on the 45 xcexcm sieve (wt %)/100)+(25xc3x97passed the 45 xcexcm sieve (wt %)/100).
The crystalline particles of 2-hydoroxynaphthalene-3-carboxylic acid having the characteristics recited in the present invention are more than 2-4.5 times as large as the conventional crystalline 2-hydoroxynaphthalene-3-carboxylic acid particles. The crystalline composition of the present invention exhibits significantly suppressed dusting tendency, and therefore, is easy for handling with significantly reduced risk to environment and human beings. Further, said crystalline particles of the present invention can easily be pulverized into fine particles and exhibit the dissolution rate comparative to the conventional small size (50-90 xcexcm) crystalline particles. That is, the crystalline composition of the present invention may preferably be used as intermediate of pigments or dyes.
The large-size crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention preferably possesses chromaticity of, 38-69 of lightness and 4.6-18.0 of whiteness.
xe2x80x9cChromaticityxe2x80x9d used herein means a property of a color stimulus determined by chromaticity coordinates or by combination of dominant wavelength or complementary wavelength and purity (JIS Z 8120).
xe2x80x9cLightnessxe2x80x9d means an attribute of a color in respect of relative contrast of the surface of an object, which is classified on the basis of white surface that is illuminated by same condition (JIS Z 8105). In the present specification and claims, xe2x80x9clightnessxe2x80x9d represents L value of the xe2x80x9cLabxe2x80x9d color representation system, which is well known in the art. The Lab values are calculated by the following formula from tristimulus values (X, Y, Z) measured according to JIS Z 8722:
L=10(Y)xc2xd
a=17.5(1.02Xxe2x88x92Y)/(Y)xc2xd
b=7.0(Yxe2x88x920.847Z)/(Y)xc2xd
xe2x80x9cWhitenessxe2x80x9d is a number of one-dimensional value representing the degree of white of the surface of an object (JIS Z 8105). In the present specification and claims, xe2x80x9cwhitenessxe2x80x9d represents the value calculated from the above described tristimulus values by the following formula:
Whiteness=Z/1.1823.
The crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention can be prepared by recrystallizing 2-hydroxynaphthalene-3-carboxylic acid at high temperature. The starting material of crystalline 2-hydroxynaphthalene-3-carboxylic acid may be prepared by any of conventional processes. For example, said starting material may be prepared by acid precipitating at 80-100xc2x0 C. 2-hydroxynaphthalene-3-carboxylic acid alkaline metal salt which is obtained by the Kolbe-Schmitt method described in Japanese Patent Publication (KOKOKU) No. 53296/1981.
The high temperature recrystallizing step may preferably be carried out immediately after acid precipitation of 2-hydroxynaphthalene-3-carboxylic acid. The aqueous 2-hydroxynaphthalene-3-carboxylic acid solution obtained by the acid precipitating step may be added with water, a water-soluble solvent or a water insoluble solvent, stirred and heated to a temperature higher than 100xc2x0 C. under pressure. The temperature and pressure may be kept for 5 to 30 minutes and then, the mixture may be cooled to 50-90xc2x0 C. After that, the solvent may be removed by centrifugation and the precipitate may be washed with water and dried to provide the desired crystalline composition.
Water, a water-soluble solvent or a water-insoluble solvent may be added to the solution independently or in combination. Examples of water-soluble solvent include methanol, ethanol, 1-propanol and isopropylalcohol. Examples of water-insoluble solvent include acetophenone, cyclohexane and ethylhexylalcohol. When the recrystallization process is carried out by adding a solvent to the aqueous solution of 2-hydroxynaphthalene-3-carboxylic acid or sodium salt thereof, said solution may contain 7-20%, preferably 8-16%, more preferably 9-13% of said acid or salt. The amount of the solvent to be added may be 2-50%, preferably, 4-40%, and more preferably 10-30% of the total amount of the aqueous solution.
The high temperature recrystallizing step may be carried out at a temperature higher than 100xc2x0 C., preferably 120-180xc2x0 C., more preferably 120-160xc2x0 C. and at a pressure of 0.1-20 kg/cm2(G), preferably 0.2-14 kg/cm2(G), more preferably 0.5-8 kg/cm2(G).
Thereafter, in the cooling step, the temperature may be declined at the rate of 4xc2x0 C./min-0.1xc2x0 C./min., preferably 2xc2x0 C./min.-0.2xc2x0 C./min.
In another embodiment, the crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention may be prepared by operating the acid precipitation process at a temperature higher than 120xc2x0 C. in the process for preparing 2-hydrocynaphthalene-carboxylic acid comprising the step of acid precipitating an alkaline metal salt of 2-hydroxynaphthalene-3-carboxylic acid. This embodiment can be practiced based on the conventional step by only raising the temperature of the acid precipitation step. Therefore, the conventional system can be easily adopted to practice the embodiment.
According to the conventional Kolbe-Schmitt method, the solution before being subjected to the acid precipitating step generally contains 7-20% of the alkaline metal salt of 2-hydroxynaphthalene-3-carboxylic acid. In this embodiment, the aqueous solution of 2-hydroxynaphthalene-3-carboxylic acid alkaline metal salt containing said amount of the salt may be stirred and heated to a temperature higher than 120xc2x0 C. under pressure, and then the pH of the solution may be adjusted to 1-4 with sulfuric acid. After the pH is adjusted, the mixture may be cooled to 50-90xc2x0 C., the solvent may be removed by centrifugation, and the residue may be washed with water and dried to provide the desired crystalline composition.
In this embodiment, the acid precipitating step may be carried out at a temperature higher than 120xc2x0 C., preferably, 120-180xc2x0 C., more preferably, 120-160xc2x0 C. When the temperature is lower than 120xc2x0 C., the particle size of the obtained crystalline 2-hydroxynaohthalene-3-carboxylic acid will be reduced and therefore, the effect to suppress dusting cannot be achieved. On the other hand, when the temperature of the acid precipitating step is higher than 180xc2x0 C., 2-hydroxynaphthalene-3-carboxylic acid may be decomposed and the yield may be declined.
The pressure during the acid precipitating step may be 0.1-10 kg/cm2(G), preferably, 0.2-5 kg/cm2(G), more preferably, 0.5-3 kg/cm2(G). The cooling step may be carried out as the same manner as in the above-described high temperature recrystallization embodiment.
In order to obtain the large size crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention, acids used in the acid precipitating step are not limited, but preferably are mineral acids or sulfuric acid. Examples of mineral acids include binary acids (hydro acids) such as hydrochloric acid and hydrofluoric acid and oxo acids such as nitric acid, phosphoric acid and perchloric acid. The pH of the acid precipitating step may preferably be adjusted between 1 and 4.
In a further embodiment, the crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention may be prepared by recrystallizing crystalline 2-hydroxynaphthalene-3-carboxylic acid obtained by means of the conventional acid precipitation process. This recrystallization may be carried out at an ambient or high pressure, and water, water-soluble solvent or water insoluble solvent may be used as above independently or in combination. Especially, a mixed solvent of water and methanol is preferable.
Generally, crystalline 2-hydroxynaphthalene-3-carboxylic acid may be prepared by means of acid precipitation of crude 2-hydroxynaphthalene-3-carboxylic acid, which may be obtained by a conventional method such as the Kolbe-Schmitt method described in Japanese Patent Publication No. 53296/1980. The crude 2-hydroxynaphthalene-3-carboxylic acid used herein is generally comprises more than 80 wt % of 2-hydroxynaphthalene-3-carboxylic acid, and impurities such as 2-hydroxynaphthalene-6-carboxylic acid, 2-hydroxynaphthalene-3,6-dicarboxylic acid and unreacted xcex2-naphthol. In order to use as an intermediate for pigments or dyes, 2-hydroxynaphthalene-3-carboxylic acid is preferably purified to 98 wt % or higher purity.
The average particle size of the crystalline 2-hydroxynaphthalene-3-carboxylic acid of the present invention is equal to or higher than 157 xcexcm, and is preferably 167-367 xcexcm. When the average particle size is less than 157 xcexcm, the effect to suppress dusting cannot be achieved. The crystalline composition may contain particles of which particle sizes are equal to or less than 74 xcexcm up to 14%, preferably, up to 6% of the total amount of the composition. When the proportion of the particles of which particle sizes are equal to or less than 74 xcexcm is more than 14%, the crystalline composition becomes to exhibit high dusting tendency due to those small size particles.
Further, the proportion of most high frequent particle size of the crystalline composition of the present invention may preferably be between 170-297 xcexcm. The proportion of the particles of which particle sizes are higher than 297 xcexcm may be 14-89%, preferably 28-80%.
Examples of the present invention will be illustrated below.